1. Field of the Invention
The present invention relates to an image forming apparatus, and more particularly, to an image forming apparatus which performs color printing by use of a plurality of photosensitive bodies.
2. Description of the Related Art
An image forming apparatus refers to an apparatus that prints an image on a printing medium, e.g., paper, according to an inputted image signal. An image forming apparatus is classified as a printer, a copying machine, a fax machine, a multi-function printer which has multiple functions of printing, scanning, copying and faxing, and the like.
An electrophotographic image forming apparatus is configured such that light is scanned to a photosensitive body charged to a predetermined electric potential to form an electrostatic latent image on a surface of the photosensitive body, the electrostatic latent image is developed into a visible image by supplying a developer to the electrostatic latent image, and the visible image is transferred onto and fused on paper. Through the above processes, the image is printed.
Of the electrophotographic color image forming apparatus, there is a so-called tandem type image forming apparatus, which includes photosensitive bodies and developing devices as many as the number of colors used in printing.
Typically, since a color image forming apparatus uses toners of four colors of yellow, magenta, cyan and black, a tandem type image forming apparatus includes four photosensitive bodies and four developing devices, corresponding to the respective colors.
In a tandem type image forming apparatus, electrostatic latent images are formed on the respective photosensitive bodies, corresponding to image information of the respective colors. Toners of respective colors are supplied to the electrostatic latent images formed on the respective photosensitive bodies from the corresponding developing devices. Accordingly, visible images are formed on the surfaces of the respective photosensitive bodies by colors. The visible images formed on the photosensitive bodies are sequentially and overlappingly transferred onto an intermediate transfer body (e.g., an intermediate transfer belt or an intermediate transfer drum), and then are finally transferred onto paper. Alternatively, the visible images formed on the photosensitive bodies are directly transferred onto paper and overlapped.
The tandem type image forming apparatus has an advantage of achieving the high-speed printing. However, because the tandem type image forming apparatus performs the color printing by overlapping the images formed on the respective photosensitive bodies by colors, image deterioration due to color mis-registration frequently occurs.
The color mis-registration occurs by composite action of various factors. Of them, a major cause of the color mis-registration is a change of a linear velocity of the photosensitive body due to runout of gears that transmit driving power between a driving source and the photosensitive body.
This kind of problem may be solved by using high precision gears. However, this solution is not preferable because there is a limitation in a process of manufacturing gears highly precisely and a great increase in costs is caused.
Alternatively, if installing driving sources on the photosensitive bodies with one-to-one correspondence, the color mis-registration due to runout of gears may be easily prevented by independently controlling the respective driving sources through a simple program. However, this solution also is not preferable because of a failure in reduction of costs.